Pool type discharge device



Feb. 14, 1939. G. DOBKE POOL TYPE DISCHARGE DEVICE Filed Feb. 24, 1957Gunthev Dobke,

Inventor:

v v6i IMAM is Attorney IIIIIIII Patented Feb. 14, 1939 PATENT OFFICE VPOOL TYPE. DISCHARGE DEVICE Giinther Dobke, Berlin -Reinickendorf,Germany,

assignor to General Electric Company, a corporation of New YorkApplication February 24, 1937, Serial No. 127,539 In Germany June 6-,1936 4 Claims.

The present invention relates to discharge devices, and moreparticularly to an improved ig nition means for such devices.

The invention is especially concerned with pool-type discharge deviceswhich are adapted to become wholly non-conductive during at least aportion of each voltage cycle. One object hereof is to provide means foreffectively and reliably controlling the restarting of such devices atdesired intervals of time. An important feature of the inventionconsists in the combination of an ignition electrode positioned innon-contiguous proximity to the cathode surface, and means effectiveduring the operation of the device to produce a copious supply ofvaporized ionizable material in the region between the ignitionelectrode and the cathode surface.

The particular features desired to be protected herein are pointed outwith particularity in the appended claims. The invention itself,however, best be understood by reference to the following descriptiontaken in connection with the accompanying drawing, in which Fig. 1 represents in longitudinal section a discharge device suitably embodying theinvention; Fig. 2 is a fragmentary section of. a modified dischargedevice embodying an alternative form of the invention, and Fig. 3 is asimilar View showing still another possible modification.

Referring particularly to Fig. 1 there is shown an enclosing envelopecomprising a sealed metal container I. This container encloses an anode2 and a pool-type cathode 3, for example, of mercury. In connection withthe anode there is provided a grid 4 and a protective shield comprisinga metal cylinder 5 surrounding the grid and anode. The anode 2 issupported and insulated from the envelope by means. of a suitableinsulator shown in the present case as a glass body 1 through which theanode lead-in connection 8 is sealed. A lead-in connection 9 for thegrid 4 may also be sealed through the glass body 'I in the mannerindicated.

Discharge devices of the type illustrated are conventionally used inrectifier or inverted circuits and when. so used are adapted to becomewholly non-conductive during that portion of the voltage cycle in whichthe anode 2 is negative with respect to the cathode 3. In order that thedischarge may be resumed at the beginning of each positive half cycle,it is necessary to provide in connection with the cathode a suitableignition means. Such means should be capable of operating reliablythrough the application of a control voltage of relatively lowpotential.

In Fig. 1 there is shown a particular ignition device constructed inaccordance with the principles of the present invention. As illustratedthis comprises an ignition electrode l0 positioned in non-contiguousproximity to the cathode surface; that is, arranged close to but out ofcontact with the cathode material. The ignition electrode [0 maycomprise a metal wire for example, of tungsten arranged within the boreof a hollow tube ll, preferably of insulating material. The internaldiameter of this tube should be sufliciently great so that a free spacewill be provided around the lead-in connection [2.

In order to facilitate the initiation of an arc when a positivepotential is impressed between the electrode EU and the cathode 3, meansis provided for generating in the region between the electrode and thecathode surface a copious supply of ionizable vapor, preferablyvaporized oath ode material.

In the particular arrangement shown this means comprises a tube 15 incommunication with the main body of cathode material and also connectingwith a chamber 16 arranged outside the discharge envelope. In connectionwith the chamber 56 there is provided a heating means M, suitably anelectrical resistance heater, surrounding the chamber. This heater maybe energized either by the current passing through the discharge device,or by means entirely independent of the main discharge. In either casethe heat which it produces will cause substantial vaporization of thecathode material contained in the chamber I6 and will cause the vaporthereby produced to be forced through an outlet tube H, the tube ii andaround the ignition electrode ID. The high vapor density thus created inthe vicinity of the ignition electrode will permit a discharge to takeplace between it and the cathode surface at a relatively low potentialon the order of a few volts. Consequently, whenever the anode 2 ispositive with respect to the cathode 3, the discharge device as a wholemay be rendered conductive by impressing a positive potential of thedesired magnitude on the ignition electrode ill. In order to prevent theinitial cathode spot from being formed on the surface of the mercury atIB instead of at 3, a construction may be provided in the tubularconnection H.

In Fig. 2 I have shown a somewhat modified form of the inventioncomprising a vapor generating device in contact with the main surface ofthe cathode material (designated by the numeral (9). In this case thevapor generating device includes an electrical resistance heater 20enclosed within an insulating sheath 2| and provided with current bymeans of a lead-in connection 22. A return circuit for the heatingcurrent is provided through the cathode material l9. In order to projectthe vaporized cathode material into the desired space a container 23having an opening 24 at the surface of the oathode is arranged tosurround the heater.

In operation, vapor issuing from the opening 24 produces a high vapordensity in the vicinity of a starting electrode comprising a thin plateor disk 25 supported adjacent to the opening. Under these conditions theact of impressing a positive potential on the starting electrode 25 willcause a cathode spot to develop approximately in the opening 24.However, the further action of the issuing vapor will cause the cathodespot to be forced away from the container 23 and will thereby preventits destruction by the action of the spot. I prefer to make thecontainer 23 of a material such as glass which is a poor conductor ofheat, or to form the container with double walls in order that verylittle heating energy will be required to produce vaporization of thecathode material.

The arrangement of Fig. 3 employs a heating device similar to thatdescribed in connection with Fig. 2. In this case, however, the ignitionelectrode comprises a plate-like portion 21 arranged at the lower end ofthe heater sheath 2| and positioned approximately parallel to thecathode surface. With this arrangement vaporization of the cathodematerial will take place in the vicinity of the ignition electrode. Dueto the confined space provided between the plate-like portion 21 and thecathode surface, the cathode spot will be driven away from the ignitiondevice by the action of the mercury vapor as soon as an arc isinitiated. In this way the ignition device as a whole will be protectedfrom the destructive effects of the cathode spot.

While I have shown particular embodiments of my invention, it will beunderstood by those skilled in the art that many modifications may bemade Without departing from the invention,

and I aim by the appended claims to cover all such modifications as fallwithin the true spirit and scope of the invention.

What I claim as new and desire to secure by Letters Patent of the UnitedStates is:

1. In an electric discharge device, an anode, a pool-type cathode and anignition device, said ignition device including the combination of anignition electrode in non-contiguous proximity to the cathode surface, acontainer enclosing a quantity of cathode material and having an openingadjacent the region between the ignition electrode and the cathodesurface, and a heater continuously effective through the opera tion ofthe discharge device to vaporize cathode material within the container.

2. An electric discharge device including the combination of an anode, apool-type cathode, an ignition electrode positioned above and out ofcontact with the cathode surface, said electrode being operableintermittently to create an auxiliary discharge to the cathode therebyto initiate a main discharge between the anode and cathode, and meansincluding an electrical resistance heater in heat-exchanging relationwith the cathode material for continuously supplying such material invapor form to the space between the cathode surface and the ignitionelectrode so as to facilitate the functioning of the latter, saidresistance heater having its conductive parts completely insulatinglyseparated from the discharge space.

3. An electric discharge device including an anode, a pool-type cathode,an ignition electrode positioned above and out of contact with thecathode surface, said electrode being operable intermittently to producean auxiliary discharge to the cathode thereby to initiate a maindischarge between the cathode and anode, means including an electricalresistance heater in heatexchanging relation with the cathode materialfor continuously supplying such material in vaporized form to the spacebetween the cathode surface and the ignition electrode so as tofacilitate the functioning of the latter, and an electrically completelyseparating insulating wall shielding the conducting parts of the heaterfrom direct contact with the discharge space.

4. An electric discharge device including the combination of an anode, amercury pool cathode, an ignition electrode comprising a plate-likeportion extending approximately parallel to the cathode surface andclosely adjacent thereto so that the cathode spot is prevented fromlodging under the electrode, and means including a resistance heater formaintaining a supply of vaporized mercury in the space between thecathode surface and the ignition electrode during the entire period ofoperation of the discharge de vice, said heater comprising a portioncontacting the cathode surface in a region underlying the plate-likeportion of the ignition electrode.

GUNTHER DOBKE.

